Stable maintenance of telomeres is critical to preserve genomic integrity and prevent accumulation of undesired mutations that might lead to various human diseases. In mammalian cells, GT-rich telomeric repeats are bound by the six-protein "shelterin" complex (composed of TRF1, TRF2, RAP1, TIN2, TPP1 and POT1) and extended by the specialized reverse transcriptase known as telomerase. The shelterin complex is essential to prevent DNA repair proteins from fusing telomeres and DNA damage checkpoint proteins from causing permanent cell cycle arrest. On the other hand, these DNA damage response factors must gain at least transient access to telomeres, since they play critical roles in both telomere protection and telomerase recruitment. Thus, the proper maintenance of telomeres involves dynamic changes between "closed" (protected) and "open" (accessible) states. However, it is still not fully understood how individual subunits of the shelterin complex are regulated to ensure proper transition of the telomere status. In addition, the critical telomere target(s) for DNA damage checkpoint proteins remain to be established. Therefore, we propose to utilize fission yeast Schizosaccharomyces pombe as a model system to investigate how telomere maintenance is ensured by collaboration among telomere specific factors and DNA damage response factors. Fission yeast should serve as an attractive model system for mammalian telomere maintenance mechanism, since the shelterin complex, telomerase components, and DNA damage response proteins are highly conserved between fission yeast and mammals. PUBLIC HEALTH RELEVANCE: Stable maintenance of telomeres is critical to preserve genomic integrity and prevent accumulation of undesired mutations that might lead to tumor formation. The overall goals of this proposal are to provide a detailed knowledge of the mechanisms that allow the telomere protection complex "shelterin" and DNA damage checkpoint sensor kinases Rad3 (ATR) and Tel1 (ATM) to work in concert to achieve stable telomere maintenance in fission yeast Schizosaccharomyces pombe. Since proteins involved in telomere maintenance and DNA damage responses are highly conserved between fission yeast and humans, we expect our findings to have major impacts in guiding future studies of human telomere regulations.